The invention relates to the method and apparatus for turning crankshaft surfaces utilizing a plurality of cutting tools of diverse characteristics.
In the machining of crankshafts for internal combustion engines a number of turning operations are utilized to produce the finished surfaces. For instance, the surfaces of a crankshaft to be machined include main cylindrical bearings, cylindrical pin bearings, radial thrust bearing surfaces, and cheek surfaces radially oriented to the crankshaft axis and axially located in substantial alignment with the ends of bearing surfaces.
To machine the plurality of surfaces it has long been common to employ a separate turning tool for each surface machined, and a plurality of tools are often used for both rough and finish turning of the same surface.
In the turning art, a variety of materials have been utilized in the manufacture of the cutting tools in order to achieve desired characteristics. For instance, the most common turning tools are formed of high-speed steel which is capable of cutting an accurate finish within close tolerances, and may be accurately shaped and contoured but high-speed turning tools require relatively slow cutting speeds, and also require relatively frequent sharpening.
The advantages of utilizing tungsten carbide cutting tools in turning operations has long been recognized as such tools are very hard and maintain a sharp cutting edge over long periods of time. Additionally, carbide turning tools permit high cutting speeds and high rates of metal removal. However, tungsten carbide turning tools are brittle, and in large sizes, are susceptible to breakage, and carbide cutting tools are difficult to contour, and are not usually utilized to produce the final configurations and surfaces desired.
To the applicants' knowledge, high-speed cutting tools and tungsten carbide cutting tools have not previously been utilized in the crankshaft turning art wherein the optimum characteristics of each type of cutting tool is utilized the maximum extent to minimize crankshaft machining time. It is recognized that crankshaft turning machines have long mounted a plurality of cutting tools upon a common tool support wherein the tools perform sequential turning operations, for instance, for rough and finish turning operations, and such as U.S. Pat. Nos. 1,919,738 and 2,191,935 discloses a plurality of turning tools for sequentially machining crankshaft surfaces.
It is also known to mount a plurality of crankshaft turning tools upon a common tool support wherein the tools are alternately used for forming cheek and bearing surfaces, and attention is directed to U.S. Pat. Nos. 2,148,293 and 2,596,511. However, known crankshaft machines of the aforementioned type utilize high-speed steel cutting tools during all phases of machining, and such prior art devices are not capable of meeting the high production demands desired from crankshaft turning machine tools presently being used.